Development of the Analog Circuit in Expendable Current Profiler

doi:10.19657/j.geoscience.1000-8527.2022.076

Abstract

Abstract:

Expendable current profiler (XCP) is an observation instrument for rapid measurement of ocean current based on the principle that ocean current cuts the geomagnetic field to produce induced electric field. When the geomagnetic field is stable, the magnitude of the induced electric field predominantly rests with the velocity of the ocean current. Therefore, the motion characteristics of the current can be explored by measuring the induced electric field originated from the ocean current. In this paper, the analog circuit used in XCP was developed, and the acquisition and preprocessing of electrode signal, compass coil signal and temperature signal in XCP were realized. The main functions of the analog circuit are as follows: (1) the multi-stage amplification of the electrode signal and the coil signal is realized through the INA128 amplification circuit; (2) considering that the frequency of the electrode signal and the coil signal is 16 Hz, a second-order band-pass filter circuit with a central frequency of 16 Hz is added to the circuit to extract the effective signal; (3) compensate hardware circuit is adopted to overcome that strong interference of the induced electric field resulted from the sinking of the XCP probe. The experimental results show that the analog circuit is stable and reliable, and it can filter the noise and extract the front-end weak signal for multi-stage amplification to meet the needs of practical applications.

Key words: expendable current profiler, development of analog circuit, signal acquisition, weak signal

CLC Number:

P631

LI Pengyu, ZHANG Qisheng, ZHOU Keyu, LIN Zucan, JIANG Xingyuan. Development of the Analog Circuit in Expendable Current Profiler[J]. Geoscience, 2023, 37(01): 107-113.

Figures/Tables 11

Fig.1 Schematic diagram of the direction of ocean current (modified from ref.[14])

Fig.2 Overall block diagram of front-end sensor and analog signal processing in XCP

Fig.3 Schematic diagram of the subtraction circuit

Fig.4 Band-pass filter circuit

Fig.5 Schematic diagram of analog to digital conversion circuit

Fig.6 Results of 5 V power ripple test (a) and -5 V power ripple test (b)

Fig.7 Resistance attenuation circuit

Table 1 Electrode channel magnification test

电路板编号	信号频率/Hz	衰减电路衰减倍数	电极通道放大倍数
1	16	3766.478343	120527.30
2	16	3735.524841	119462.09
3	16	3769.317753	111209.96
4	16	3732.736096	115752.14
5	16	3756.574005	119083.40
6	16	3769.317753	111209.95

Table 2 Coil channel magnification test

电路板编号	信号频率/Hz	线圈通道放大倍数
1	16	2529
2	16	2704
3	16	2655
4	16	2623
5	16	2769
6	16	2600

Fig.8 Coil channel output waveform

Fig.9 Voltage comparator test

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